Wheels out West: The Galway Bike Sharing Scheme
February 10, 2020 by Philip Lowney

Overview

In this post, I study the performance of the Coca Cola Zero Bikes scheme in Galway based on data collected throughout 2019. We will:

  • Attempt to visualise the behaviour of the scheme through animation
  • Present daily profiles of the scheme in terms of key metrics
  • Identify the daily geographic flow trends of the scheme
  • Identify which stations which are performing best and worst with respect to availability of bikes

Thanks is due to An Rothar Nua, the operators of the scheme, who kindly granted me permission to poll their API.

Contents

Introduction

The Galway bike sharing scheme was rolled out in November 2014 and is operated by the An Rothar Nua consortium on behalf of the National Transport Authority. Funding was provided by both Coca Cola Zero, the commercial sponsor of the scheme, and the Department of Transport, Tourism and Sport. At time of writing, the scheme is composed of 23 stations, 21 of which are open. The scheme was launched with a stock of 195 bikes .

The data herein was obtained by regularly polling a web service provided by An Rothar Nua, which SchemeStats polls once every minute. The data presented is based on polling conducted throughout the 2019 calendar year. Figures for bikes in transit and utilisation are both estimates performed by SchemeStats based on the real-time station population figures. More about the methodology for determining these figures can be found in the About section.

Caveat: Data Consistency

The data herein, while covering the majority of 2019, is somewhat partial. Unfortunately, a couple of bugs on the collection engine meant that data for about 10% of the year was not collected. Since SchemeStats polls a realtime API with no history, any missed poll cannot be recovered. It takes a year to collect a year, about a half a million minute-by-minute polls, so it seems a waste not to report the figures, such as they are. I have included coverage per month of 2019 in the appendix. Data for >90% of the year was collected as intended.

Animating One Week in Galway

What follows is a time-lapse animation of the population of each station over a one-week period from Monday October 7th to Sunday October 13th 2019. I picked this week because it is somewhat recent, the schools are back, people are typically not on holiday, and it is not so cold that cyclists are dissuaded. The video is composed of frames separated by 5 minutes of elapsed time. Each cylinder is plotted at the location of a station, and its height represents the number of bikes in a station. Red ‘stubs’ represent empty stations, and red full-height cylinders are closed stations. Note that during the early morning period the scheme is closed, hence the apparent disappearance most of the cylinders. This is simply a peculiarity of the way bikes are reported during closed periods by the An Rothar Nua API. The histogram towards the bottom right is the distribution of station populations, with bars on the left representing emptier stations. The heat-map in the bottom right is the net change over the last 30 from the time on the main map, with blue dots for stations losing bikes and red for those gaining bikes.

Some observations of the video:

  • Utilisation seems low.
  • There is no strong trend in terms of geographic draining and filling up with bikes.
  • Bikes appear well distributed, with most stations having bikes most of the time.

Day Profiles

A ‘Day Profile’ is a plot of the average values of a given metric on a given day of the week – e.g. ‘Available Bikes on Tuesdays’. In the case of Galway, these are explored between the hours of 6 AM and midnight. I’m also overlaying the trend with the standard deviation – a measure of the spread of the data - to get an idea of how noisy the signal is. In the charts below, the solid lines are averages, and the shadow on either side of them is the standard deviation range. I’ve elected to plot values between 6 AM and midnight, as there is no data when the scheme is closed.

Bikes in Circulation

This estimated figure yields the following day profiles for 2019:

Bikes in Circulation per Day, 6AM to Midnight

Empty Stations

We can also form a picture of the measures of the number of stations which are empty per day:

Day Profiles for Empty Stations, 6AM to Midnight

Day Profile Analysis

Average numbers of bikes in circulation, albeit estimated, rarely exceed 6. This is less than half that observed in Cork and a fraction that observed in Dublin. There does not appear to be a significant bias to usage at any time of day either.

Empty station profiles indicate that stations are rarely empty, a good indication for those few users of the scheme.

The day profiles do not show a tendency to change significantly over the course of the day, suggesting usage levels sufficiently low that the scheme is not burdened at any point during the day.


A Note from the Author

I really hope you find the tools and blog posts provided here useful. This website is a hobby I undertake in my spare time. If you have enjoyed using this site, please consider sharing it on a platform of your choice. Knowing this project is useful to people spurs me on to provide further functionality and content. If you have any recommendations, please don’t hesitate to get in touch via the feedback link above.

Thanks,

Philip


Weekday Flows

Using SchemeStats’ ‘Metrics Map’ tool, it’s possible to plot the geography of a given station measure, for a given time period. That time period can either be a simple from- and to- value, or a slice of a day. So we can plot things like ‘Show us the average net change of all stations between the hours of 7AM and 10AM, Monday to Friday, for 2019’. This is what I’ve done below for two times of the day during the week when the scheme may be used by commuters as we see elsewhere. If we see the same stations filling up in the evenings that also emptied in the mornings, it’s likely people are using them to get to and from their place of work or study.

Morning Trends

Here is the average net change between 7AM and 10AM, Monday to Friday for 2019:

Weekday average net change between 7AM and 10AM

We observe very small average figures here – the biggest gainer over this period is gaining only two bikes, and the one losing the most (i.e. the darkest blue) is only gaining a little under 2 bikes on average.

Evening Trends

Here is the average net change between 4PM and 7PM, Monday to Friday, for 2019:

Weekday average net change between 4PM and 7PM

Again, the ranges here are very small. The darkest red below is a gain of just one bike, and the lightest blue is a loss of only 3 bikes.

Weekday Flow Analysis

The numbers entering and exiting different parts of the city at typical commuting periods are very small, so this is not a scheme used significantly by commuters in Galway. However, it is also clear from the charts above that there is a symmetry between the mornings and evenings – those stations losing bikes early in the day gain them again later, and vice versa. This suggests that there is small number of people using the scheme to get to and from places of work.

Station Performance

Using the same machinery from the Metrics Map, we can determine how much of the time stations spend empty. I’ve created a plot of the percentage of time stations spend empty between 6AM and midnight. Unlike in previous posts, I have not drawn separate graphs for weekends, or for different times of day on a weekday, as the evidence of the day profiles indicates that there is not much difference between different times of the day or different days of the week. A full breakdown of percentage of time spent empty per station is provided in the appendix.

Here is the plot of the percentage of time spent empty, all week, 6AM to midnight for 2019:

Here are the five best and worst performing stations by percentage of time spent empty:

Best 5 Stations by Percentage of Time Empty

Station

Mean % of Time Empty

Merchants Gate

1.13

Headford Road

1.15

Brown Doorway

1.38

New Dock Street

1.76

Claddagh Basin

1.8

 

Worst 5 Stations by Percentage of Time Empty

Station

Mean % of Time Empty

Newtownsmith

21.42

Galway City Hall

8.28

Gaol Road

8.23

Cathedral

8.05

Park & Ride NUIG

7.25

Station Performance Analysis

Figures for amount of time spent empty and full across the whole scheme are very favourable – it seems that users stand an excellent chance of obtaining bikes from most stations most of the time.

Data Summary

The data presented in this post may be summarised as follows:

  • The scheme is not used extensively for commuting, with estimates of bikes in circulation rarely exceeding 6 on average.
  • Availability of bikes is excellent, with stations rarely empty. Newtownsmith is an exception here, spending a fifth of the time empty on average.
  • Different days of the week do not show significantly different trends in terms of bikes in circulation.
  • Despite the underutilisation of the scheme by commuters, there does appear to be a weak, symmetrical inward and outward- flow of a few bikes in the mornings and evenings respectively.

Appendix

1: Polling Coverage

As mentioned, data collection for the year did not cover 100% of elapsed time. The following table details the monthly counts of minute-by-minute polls for 2019 collected by SchemeStats. Total coverage was 90.82% for the year.

Month

Actual Polls

Target Polls

Coverage, %

January

17837

44640

39.96

February

40225

40320

99.76

March

44614

44640

99.94

April

43176

43200

99.94

May

44599

44640

99.91

June

42411

43200

98.17

July

36856

44640

82.56

August

37335

44640

83.64

September

41446

43200

95.94

October

41430

44640

92.81

November

42796

43200

99.06

December

44624

44640

99.96

       

Totals

477349

525600

90.82

 

2: Time Spent Empty per Station, 6AM to Midnight, 2019

Station

Mean % of Time Empty

Std. Deviation

Merchants Gate

1.13

8.37

Headford Road

1.15

7.78

Brown Doorway

1.38

9.52

New Dock Street

1.76

10.02

Claddagh Basin

1.8

9.39

Lough Atalia

1.97

9.73

Sacred Heart (Seamus Quirke Rd)

1.99

8.56

Father Burke Road

2.69

10.99

County Hall

3.09

13.45

Wood Quay

3.31

12.25

Eyre Square South

3.44

12.23

Bodkin

4.16

17.2

Glenina

4.6

15.33

Kingfisher, NUIG

4.7

13.02

Fairgreen

4.75

15.45

Mainguard Street

5.29

16.27

O'Shaughnessy Bridge

5.78

16.44

University Hospital Galway

5.86

19.64

Park & Ride NUIG

7.25

17.04

Cathedral

8.05

19.88

Gaol Road

8.23

23.53

Galway City Hall

8.28

20.92

Newtownsmith

21.42

39.8